Simply put, Iceland is one giant geological hotspot. The country is one of the most active volcanic regions around, with eruptions occurring every 3–4 years on average. But why is Iceland so active? It’s mostly due to its location on the Mid-Atlantic Ridge, where the Eurasian and North American plates are moving apart – and therefore literally opening the earth’s crust. In the center of this ridge sits Þríhnúkagígur volcano. The most north-easterly of the three peaks is a small cinder cone, standing about 35 m/100 ft higher than its surroundings. At the top of this cone is a funnel-shaped opening, about 4×4 m/12×12 ft wide, the entrance of a huge 120 m/400 ft deep, bottle-shaped volcanic vault, measuring 50×70 m/160×220 ft at the bottom. Volcanic passages continue down to the southwest, to a total depth of about 200 m/700 ft.